In conventional AM (amplitude-modulation) optical transmission techniques a D.C. level, or pedestal, is transmitted in conjunction with an amplitude-modulated carrier. The D.C. level, however, does not contribute any information to the transmitted AM-signal. Furthermore, transmission of the D.C. level increases the amount of power necessary for transmission of the AM-signal, thereby having an adverse impact on the efficiency of the conventional AM scheme.
FIG. 1A illustrates the waveform of the output signal of a conventional AM modulator. A D.C. level 101 is implicit in this signal. As a consequence, the power transmitted is unnecessarily increased and the efficiency of the conventional AM system is degraded. FIG. 1B illustrates one modulation cycle of a signal transmitted from a conventional AM transmitter. Cross-hatched area 100 represents the energy (E) transmitted, which is expressed as: ##EQU1## The transmission of unnecessary energy may prove disadvantageous in many applications, and it is thus an object of the invention to provide an energy-efficient modulation technique, and also a corresponding demodulation technique.